This invention relates to a detecting system for detecting the proximity of an aircraft to the system and more particularly to a detecting system for determining whether an aircraft is within a particular distance and altitude from the system. The detecting system is particularly useful to give an indication whether or not an aircraft is within close proximity of an automobile in which the detecting system may be placed to determine whether the aircraft has the capability of tracking the automobile speed in an aircraft speed detection and ticketing operation.
Traffic control by the state or local authorities has recently developed into the use of radar speed detecting systems for measuring the speed of vehicles as they travel along public roads or highways. In this way, the authorities can easily determine whether a particular vehicle is exceeding the speed limit and would therefore be subject to ticketing for a traffic violation. In response to such systems, radar detecting units have been developed for use by motorists to determine when a radar speed detection system is being utilized in the vicinity of a vehicle being driven along the public roads or highways. In this way, the motorist can detect the use of radar speed detection equipment and adjust the speed of the vehicle to conform to the posted speed limit in the event that the speed limit is being exceeded to thereby avoid costly traffic violations.
As the authorities have recognized, the use of radar detecting systems inhibits the effectiveness of this method for regulating and controlling the flow of traffic on public roads and highways. There have thus been increasingly complex radar speed detection systems developed for enhancing the effectiveness of these procedures as well as other methods not requiring complex and expensive systems. In one method, the authorities may determine the speed of vehicles traveling on the public roads or highways by use of an aircraft which will fly at an elevation above the flow of traffic. The flow of traffic can be observed and the traveling of individual vehicles can be measured as to the time in which it takes a vehicle to traverse a predetermined distance so as to give an indication of the speed at which the vehicle is traveling. If it is found that a vehicle is traveling at speed exceeding the posted speed limits, the aircraft can then relay the information to the ground unit wherein the vehicle can be detained and ticketed for the violation of the traffic regulations.
In such aircraft speed detection and ticketing operations, the roadway may be marked with appropriate designations so that the authorities in the aircraft can determine when a particular vehicle has traversed a predetermined distance such as a number of miles or portions thereof. The time in which the vehicle traverses this distance can be measured from the aircraft and thereafter the speed of the vehicle can be determined very accurately. With this method, the driver of the vehicle will not be aware of the aircraft's presence and has no means by which the aircraft's presence can be determined. It has also been found that in other situations, such as the flying of privately owned aircraft or the like, that the presence of other aircraft in the vicinity thereof would be desirable information for the pilot of the individual aircrafts. Although it is assumed that the air traffic controller at an airport in the vicinity of any airborne aircraft would have notified the pilots if another airplane is in the vicinity thereof, such information is not otherwise readily obtainable by the pilots of aircraft unless they have an on-board radar system. In most cases, the aircraft is not equipped with any radar equipment and information on other aircraft in the vicinity of the flight path of an individual aircraft would be extremely beneficial to the pilot thereof.
There are various systems which have been found in the prior art for detecting the proximity of aircraft or the like near a predetermined region. Such systems have been extremely complex and are not able to be utilized by the common market. One such system is found in U.S. Pat. No. 4,318,102 which shows an intrusion detecting system yieldinq range and altitude measurements of aircraft or the like in the vicinity of an area to be secured. It is clear that such a system is mainly usable by the armed forces of a governmental entity for surveillance of the air space over the perimeter of a secure area. In this system, an RF perimeter intrusion detecting system for measuring both range and altitude of aircraft or the like which transgress the air space over a protected area is disclosed. The system includes a first receiver forming a monostatic radar and RF transmitter and a second receiver forming a bistatic radar system. A lookup intruder sensor comprising an upward looking guided wave structure around a secured area perimeter may be used as the transmitting and receiving antennas for the radar system. Once an aircraft or the like is detected by the radar system, processing equipment will derive both elevation and range information on the intruding aircraft. It is clear that this system is an extremely complex radar system to indicate breach of secured areas by unauthorized or hostile aircraft or the like. Such a system as well as virtually any radar system is not feasibly usable as means for detecting aircraft which may be part of an aircraft speed detection and ticketing operation or by aircraft to determine the proximity of other aircraft in the vicinity thereof.
Similarly, as seen in U.S. Pat. No. 3,320,616, there are known systems for detecting and monitoring the orbiting satellites which may be positioned above the planet in space. As seen in this patent, a thin wall of CW energy is erected to extend upwardly and satellites crossing through this energy will reflect a portion thereof for reception in radio interferometer equipment placed on the ground. The elevation of any satellite passing through the thin wall of CW energy may be computed from two electrical signals which are representative of the angular position of the satellite with respect to two receiver sites. Again, it is noted that complex equipment and calculations are necessary to determine the elevation of an orbiting body or the like. Clearly, such a system is not usable to provide altitude information to a common user for detecting the presence and proximity of an aircraft in the vicinity thereof.
It is known that airport and air traffic controllers have at their disposal complex radar systems for tracking and maintaining communication with various aircraft in the vicinity thereof. As more and more aircraft are present in the skies, increasing problems in maintaining safe and effective control over the flights of these aircraft have necessitated regulation which facilitates the detection and tracking of various aircraft by an air traffic controller.
Presently, an identification number comprising of four digits is assigned to any FAA licensed aircraft by the air traffic control system and the number can be changed from time to time by the controller. A transponder aboard the individual aircraft is initiated by impingement of radar signals directed outwardly from one or more air traffic control stations over the region in the vicinity of those stations. When initiated, the transponder will send a burst of data back with the reflected radar signal to the radar reception system and air traffic controller. The burst of data sent from the transponder includes the identification number currently assigned to the aircraft and includes information reflecting the reading of the aircraft's altimeter such that the air traffic controller can identify the aircraft as well as pin point its position and altitude. It should be evident that the burst of data directed from the transponder is not only sent back to the radar detection system with the reflected radar signals, but is omnidirectionally sent out from the transponder upon initiation by the radar sweep.